1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device which has a function of supplying a current to a load. Further, in particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device which has a function of controlling, with the use of a transistor, a current to be supplied to a load. Further, in particular, one embodiment of the present invention relates to a display device or a light-emitting device which includes a pixel including a display element whose luminance depends on a signal and a signal line driver circuit and a scan line driver circuit which drive the pixel, a driving method thereof, or a manufacturing method thereof. Further, one embodiment of the present invention relates to an electronic device having the display device in a display portion.
2. Description of the Related Art
In recent years, self-luminous display devices, light-emitting devices, and the like including light-emitting elements such as electroluminescence (EL) elements in pixels have attracted attention. As examples of such a light-emitting element used in such a self-luminous display device, an organic EL element and an inorganic EL element are known. These light-emitting elements emit light by themselves; thus the visibility of an image displayed by a display device including the organic EL element or the inorganic EL element is higher than that of an image displayed by a display device including a liquid crystal element. Further, the organic EL element and the inorganic EL element have advantages such as unnecessity of a backlight and high response speed. Note that the luminance of many of light-emitting elements is controlled by the value of current flowing to the light-emitting element.
In addition, active matrix display devices in which each pixel is provided with a transistor that controls light emission of a light-emitting element have been developed. The active matrix display devices have the following advantages, for example: high-definition display and large-screen display which are difficult to achieve in passive matrix display devices can be achieved and they can operate with less power consumption than passive matrix display devices.
FIG. 14 illustrates a configuration example of a pixel in a conventional active matrix display device (see Patent Document 1). The pixel in FIG. 14 includes a first transistor 11, a second transistor 12, a capacitor 13, and a light-emitting element 14. The first transistor 11 is connected to a signal line 15 and a scan line 16. A power supply potential Vdd is supplied to one of a source electrode and a drain electrode of the second transistor 12 and one electrode of the capacitor 13.
As another example, the configuration and the operation method of the pixel in FIG. 15 are suggested in Patent Document 2. The pixel in FIG. 15 includes a first transistor 21, a second transistor 22, a capacitor 23, and a light-emitting element 24, and the first transistor 21 is connected to a signal line 25 and a scan line 26. The second transistor 22 serving as a driver transistor is an n-channel transistor, a ground potential is supplied to one of a source electrode and a drain electrode of the second transistor 22, and Vca is supplied to a cathode of the light-emitting element 24.
FIG. 16 shows a timing chart for operating the pixel. In FIG. 16, one frame period is divided into an initialization period 31, a threshold voltage (Vth) writing period 32, a data writing period 33, and a light emission period 34. Note that one frame period corresponds to a period for displaying an image for one screen, and the initialization period, the threshold voltage (Vth) writing period, and the data writing period are collectively referred to as an address period.
Patent Document 3 discloses another example of a pixel.